Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $208.29   13.273%   $235.9363   $235.94   $235.95   $235.90  
  Purchase #2 $46.92   11.724%   $52.4209   $52.42   $52.40   $52.40  
  Purchase #3 $175.32   11.523%   $195.5221   $195.52   $195.50   $195.50  
  Purchase #4 $216.63   12.836%   $244.4366   $244.44   $244.45   $244.40  
  Purchase #5 $122.90   11.630%   $137.1933   $137.19   $137.20   $137.20  
  Purchase #6 $127.81   12.840%   $144.2208   $144.22   $144.20   $144.20  
  Purchase #7 $70.48   10.463%   $77.8543   $77.85   $77.85   $77.90  
  7 purchase totals = $968.35       $1,087.5843   $1,087.58   $1,087.55   $1,087.50